Work-related musculoskeletal disorders (WMSD) account for one in three lost work time illnesses. In spite of epidemiological evidence for a positive relationship between exposures to repetitive and/or forceful motion and the prevalence and incidence of WMSD, the mechanisms of pathophysiology are incompletely understood. Animal models provide an opportunity to examine the effects of these tasks on tissues under controlled experimental conditions. To date, we have explored the effect of repetitive and/or forceful reaching in young adult rats, and have clearly shown that higher task demands lead to tissue injury and inflammation, followed by fibrosis. In this 3 year study, we will extend our model to consider the effects of aging. We will use qualitative and quantitative histological and immunochemical techniques, and behavioral tests of motor and psychosocial function to address the following specific aims related to exposure of aged rats to repetitive, low force reaching and grasping. SPECIFIC AIM I: To determine the extent to which exposure to two task regimens, high repetition-low force (HRLF) and low repetition-low force (LRLF) causes tissue injury, inflammation, fibrosis and degeneration in musculoskeletal and neural tissues of the upper extremity in aged rats. SPECIFIC AIM II: To determine the extent to which exposure to the two task regimens (HRLF, LRLF) causes declines in motor performance in aged rats. SPECIFIC AIM III:To determine the extent to which exposure to the two task regimens (HRLF, LRLF) causes psychosocial behavior dysfunction in aged rats. Examination of localized tissue and humoral responses in aged rats following exposure to repetitive will make important contributions to occupational health practice. Our previous work shows that tissue pathophysiology in early WMSD development is inflammatory and dose-dependent. We hypothesize that tissue tolerance declines over time if task exposures are sufficient to overload tissues and cause repeated injury/inflammation leading to tissue fibrosis, degeneration and long-term disability. We also hypothesize that age-related tissue changes will further affect tissue tolerance, thus amplifying declines in tissue tolerance leading to greater motor and behavioral dysfunctions.Through the use of our animal model, we have an opportunity to test our hypothesis regarding the effects of risk factors on tissue and function in aged rats in order to provide insight into effective prevention and management of WMSD in older adults.